This invention relates to channel selecting apparatus for use with two tuning devices and, more particularly, to channel selecting apparatus which is provided with a common channel selector by which the two tuning devices can be tuned to the same channel at the same time, but is further operable to lock the tuning condition of one of the tuning devices while enabling the channel selector to be operated so that the tuning condition of the other tuning device can be changed, as desired, without affecting the locked tuning condition of the first-mentioned tuning device.
In some applications, it is desirable to provide two different tuners which are capable of being operated independently of each other to receive different broadcast frequencies. For example, in the signal recording art, one tuning device may be provided in a signal receiver so that a user can perceive signal information which is received thereby, and another tuning device may be provided in a signal recorder so that, while the user perceives that signal information, such information also can be recorded. Of course, if two different tuning devices are provided, that is, one tuning device is provided for signal reception so that the information can be reproduced and the other tuning device is provided for signal recording, the user may wish to record signal information which is received via one channel while perceiving information which is received via a different channel.
One example of the foregoing is found in video tape recorders (VTR's) which are used with television receivers. Thus, the user may wish to view one television program on the television receiver while a different television program is recorded by the VTR. Since the television receiver and the VTR both include separate, independent tuners, it is not necessary that both devices be tuned to the same channel to enable a proper video recording operation. However, while the tuner included in the television receiver can be changed as desired, it is necessary that the tuner in the VTR be locked to the channel which is being recorded throughout the duration of a recording operation. If the tuning condition of the tuner in the VTR is changed while video signals are being recorded, either deliberately or unintentionally, the recorded signals will be distorted. Furthermore, unintentional adjustments to the tuning condition of the tuner in the VTR may result in the recording of an unwanted program.
In order to facilitate a change in the tuning condition of the tuner in the television receiver, while preventing a concurrent change in the tuning condition of the VTR, separate channel selectors generally are provided for both devices. Even when the television receiver and VTR are combined in a common housing, or cabinet, a separate channel selector is provided for the television receiver, and another separate channel selector is provided for the VTR. The user may, therefore, select a particular channel for recording by the VTR by operating the VTR channel selector, and then may monitor that program being recorded or may view any other channel by operating the channel selector of the television receiver. The use of such two different channel selectors is believed to reduce substantially the possibility of a user unintentionally changing the tuning condition of the VTR during a recording operation.
With the advent of electronic tuners, many of the disadvantages of prior art electromechanical tuners have been avoided. An electronic tuner generally may include a variable reactance device, such as a varactor, whose reactance is determined by a control voltage applied thereto. The reactance of the variable reactance device establishes the tuning condition of the electronic tuner, and thus the particular channel to which the tuner is tuned. In some electronic tuners, the control voltage which is applied to the variable reactance device is produced in response to the manual operation of channel selector switches, such as locking, non-locking or touch-sensitive switches. When used in television receivers, the electronic tuner of the aforedescribed type is simple to operate, enables virtually any channel to be selected rapidly, and exhibits a high longevity while requiring little or no maintenance. The typical electromechanical tuner which is replaced by this electronic tuner includes many contacts and detents which may oxidize and which, over prolonged usage, may become worn, thereby degrading the tuning condition. Furthermore, the electromechanical tuner often is difficult to operate. Also, the electromechanical tuner cannot be used to select arbitrary channels directly. Rather, channels must be selected in sequence until a desired channel is obtained.
The relative difficulty is operating the electromechanical tuner has one advantage when used as the tuner in a VTR. That is, there is a lesser probability that the electromechanical tuner will be operated to change the tuning condition of the tuner during a recording operation. For this reason, most VTR's generally are provided with an electromechanical tuner and not with an electronic tuner.
Nevertheless, the use of separate channel selectors in the television receiver and in the VTR is a duplication of parts. Although separate tuning devices are necessary in order to permit different channels to be recorded and to be viewed, the requirement heretofore of redundant channel selectors has added to the cost of manufacture and assembly of television receivers and VTR's. This is particularly so when the television receiver and VTR are combined in a single housing or cabinet. However, it has been thought heretofore that separate channel selectors still are necessary in order to prevent a change in the tuning condition of the VTR during a recording operation, while permitting the tuning condition of the television receiver to be changed as desired. It also has been thought that, in general, a user of the VTR may select a particular channel for recording without wishing to monitor that channel on the television receiver. This is achieved by operating the channel selector of the VTR to the desired channel for recording, while operating the channel selector for the television receiver to select any other desired channel for viewing. It is believed, however, that a user will, in practically all instances, monitor, at least preliminarily, the channel which is selected for recording.
Therefore, there is a need for providing a single channel selector which is common both to the tuner of a television receiver and to the tuner of a VTR, thereby minimizing the number of parts in the channel selecting apparatus, and thus reducing costs. Furthermore, if a common channel selector is provided for both tuning devices, there is an additional need that, although both tuners may have their tuning conditions adjusted simultaneously, the tuner of the VTR must be locked to a selected channel during a recording operation, even though the tuning condition of the television receiver might be changed.